Property Plant Equipment and Mineral Rights and Reserves (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Property plant equipment and mineral rights and reserves
Mineral rights and reserves	$ 41,861	$ 51,435
Land	13,881	11,591
Buildings and improvements	95,388	86,410
Machinery and equipment	362,043	352,768
Construction in progress	24,907	15,173
Gross property, plant and equipment	$ 538,080	$ 517,377

Gross amount, as of the balance sheet date, of long-lived, depreciable assets that include building structures held for productive use including any addition, improvement, or renovation to the structure, such as interior masonry, interior flooring, electrical, and plumbing.

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Carrying amount at the balance sheet date of mineral rights, or rights to extract a mineral from the earth or to receive payment in the form of a royalty for the extraction of minerals, net of amortization.

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- Definition

Gross amount, at the balance sheet date, of long-lived physical assets used in the normal conduct of business and not intended for resale. This can include land, buildings, machinery and equipment, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software.

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